Found in old American documentation, this circuit is current as it uses the 555 to modulate an infrared LED. Pulses are set by R1.
Featuring low output impedance and high input impedance, this configuration was found in a 1980s...
In the figure we have a TTL logic interfacing circuit as CMOS logic using a 6N139 optocoupler...
We found this circuit in an English documentation from 1989. The integrated circuit used is not...